Uttar Pradesh Technical University (UPTU) 2007 M.C.A Cryptography & Networks Security - Question Paper
PAPER ID: 1476 Roll No.
(Following Paper ID and Roll No. to be filled in your Answer Book)
Printed Pages : 4 MCA - 404(2)
(SEM. IV) EXAMINATION, 2006-07 CRYPTOGRAPHY & NETWORKS SECURITY
Time : 3 Hours] [Total Marks : 100
Note : Attempt all questions.
1. Attempt any four out of the following :
(a) What is denial of service attack? 5
(b) What is Trojan Horse? What is the principle 5 behind it?
(c) What is repudiation? How can it be 5 prevented in real life?
(d) Let C be a block cipher of block size n : 5
(i) How many different block values are possible?
(ii) How many different permutations of blocks are possible?
(iii) If C is not an arbitrary permutation, but has key length k, how many trials will be required to break c through exhaustive key search.
(e) While DES keys are 64 bites long, but its 5 effective key length is only 56 bits, why?
(f) What is the most security - critical component 5 of DES round function. Give a brief description
of this component.
2. Attempt any four parts of the following:
(a) What is the idea behind meet in the middle 5 attack? How it can be avoided in 3 DES?
(b) What is the difference between block cipher 5 and stream cipher? What are the different modes of block cipher operation? Explain any
one of them.
(c) Draw a diagram of cyclic encryption being 5 used to generate pseudo-random Numbers.
(d) Consider the diffic-Hellman scheme with a 5 common-prime q = 11 and primitive root
a = 2
(i) Show that 2 is indeed a generator
(ii) If the user A has public key YA = 9 what is As private key?
(iii) If the user B has public key YB = 3 what is the secret key k in between A and B.
(e) Explain Blowfish in detail. 5
(f) Discuss the vulnerability of DES 5
3. Attempt any two out of the following:
(a) Assume you have a secret that you encrypt 10 and publically post the cipher text. You use
a 56 bit keying variable and then split the keying variable into two equal - size nonoverlapping. Segments of 28 bits each. You give one of these segments to Trustee A and give the other to Trustee B. If one of these trustees tries to break the cipher, how many keying variables would the trustee have to key an advantage in order to be successful?
(b) Write extended Euclid algorithm and find 10 the value of the following:
(i) 471395 mod (48)
(ii) 43207 moj (1024)
(iii) 257 mod (123)
(c) Write RSA algorithm if N = 187 and the 10 encryption key E=17, find out the corresponding private key.
4. Attempt any two out of the following:
(a) Alice is using a toy version of the DSS 10 signature scheme with a prime modulus P = 47 and generator g = 2 of order q = 23. By accident, slice generates signatures for two different messages with the same per-message random number K. The hash codes of two signed messages are 2 and 3 and signatures are (4, 21) and (4,19) respectively, compute slice private key.
transmitted in pretty good privacy (PGP) protocol? Explain with clear diagrams.
(c) Describe the properties of a cryptographic 10 hashing function. Clearly describe how a cryptographic hashing function can be implemented using a block cipher.
5 Attempt any two parts out of the following :
(a) Describe the man-in-the middle threat in 10 secure shell and investigate which authentication options it offers.
(b) List the characteristics of a good firewall 10 implementation ? How is a circuit gateway different from an application gateway ?
(c) Describe the role of Ticket granting server 10 (TGS) in kerberos authentication protocol.
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